Figure 1.

Rearrangement of the MCM double hexamer during helicase activation. The double hexamer that initially surrounds double-strand DNA is reconfigured during activation to yield two active helicases surrounding single stranded DNA. In one mode (left), the Mcm2-7 hexamers become positioned in a C–>N direction on each of the 5′ to 3′ strands and move away from each other. In the other mode (right), the Mcm2-7 hexamers become positioned in a N to C direction on the 5′ to 3′ strands and move past each other toward the fork junctions.